Subject: Re: [PATCH] Enable backlight when trigger is activated

From: Pavel Machek <[email-masked]>
Date: Wed, 24 Jul 2019 10:33:55 +0200

Hi!

> >>> +++ b/drivers/leds/trigger/ledtrig-backlight.c
> >>> @@ -114,6 +114,8 @@ static int bl_trig_activate(struct led_classdev *led)
> >>>  	n->old_status = UNBLANK;
> >>>  	n->notifier.notifier_call = fb_notifier_callback;
> >>>  
> >>> +	led_set_brightness(led, LED_ON);
> >>> +
> >>
> >> This looks fishy.
> >>
> >> Maybe you should use a default-state = "keep" instead? (and you'll have
> >> to support it in the LED driver).
> >>
> >> That'll give you proper "don't touch the LED if it was turned on" behavior,
> >> which is what you seem to want.
> > 
> > Actually no, that's not what I want. LED should go on if the display
> > is active, as soon as trigger is activated.
> > 
> > Unfortunately, I have see no good way to tell if the display is
> > active (and display is usually active when trigger is activated).
> 
> default-state DT property can be also set to "on"
> (see Documentation/devicetree/bindings/leds/common.txt).

Yes, except that it does not work with all drivers :-(. In particular,
it does not work with lm3532.

We should really move more of the device tree parsing into core, so
that there's one place to fix...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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